1. Field of the Invention
The present invention relates generally to chemical mechanical planarization (CMP) and electroplating of a metal film on semiconductor devices, and more particularly, to a method and apparatus for reclaiming a metal from the effluent of a CMP process and using said reclaimed metal in an electroplating process.
2. Description of Related Art
Electroplating or electrodeposition, is a well-known process used to deposit metals such as copper from a chemical solution onto an electrode called a cathode and is described in the following articles, that are hereby incorporated by reference:
1. Loweheim, F. A., ed., Modem Electroplating, 3rd edition, Electrochemical Society, 1974.
2. Paunovic, M. and Schlesinger, M., Fundamentals of Electrodeposition, Electrochemical Society Series, John Wiley and Sons, 1998.
Electroplating has recently received a tremendous amount of attention as a process for depositing a metal such as copper onto the surface of a semiconductor device. Prior art FIG. 1 is a schematic representation of the typical components of an electroplating system. In this representation, an electroplating chemical solution 205 is fed from a larger storage chamber (not shown) into an electroplating chamber 210. The electroplating chamber 210 contains an anode 215 and a cathode 220, both of which are immersed in the chemical solution 205. The anode 215 and cathode 220 may be constructed of copper, platinum, carbon, steel, or other conductive materials typically used for electrodeposition. Electricity is generated from a power source 225 and is passed between the anode 215 and cathode 220 such that electrons flow from the anode 215, through the wire 230, to the cathode 220. The power source 225 may be a battery, a potentiostat or other potential creating device that is well known in the industry.
As is well known in electrodeposition, this will cause a reduction reaction to occur at the cathode 220 and an oxidation reaction to occur at the anode 215. In electroplating, the reduction reaction is a chemical reaction where a species which is on the surface of the electrode, or is dissolved in the chemical solution 205, such as a positively charged metal ion (M+), gets reduced, i.e. charged by at least one electron as represented by the following reaction:
M++exe2x88x92xe2x86x92M 
This causes the metal (M) to become xe2x80x9cplatedxe2x80x9d onto the cathode so that a metal film is grown onto the surface of the cathode 220. The metal may be any conductive material such as copper, tungsten, aluminum, iron, nickel, titanium, tantalum, palladium, iridium, platinum, silver, or metal alloys. In the semiconductor industry, a semiconductor wafer containing semiconductor devices is typically used as the cathode 220 causing a film of metal to become plated onto the semiconductor devices on the wafer.
An oxidation reaction is a chemical reaction where a species at the anode 215 gives up at least one electron. The species in an oxidation reaction might be a species in the chemical solution 205 such as negatively charged ions (Anxe2x88x92) which become oxidized as represented by the following reaction:
Anxe2x88x92xe2x86x92An+exe2x88x92, 
The species in an oxidation reaction might also be the metal material of the anode 215. In this case, during processing the metal loses at least one electron and becomes dissolved in the chemical solution 205 as is represented by the following reaction:
Mxe2x86x92M++exe2x88x92
CMP is a well-known process used to remove and planarize materials on a semiconductor device such as copper, tungsten, aluminum, silicon, silicon dioxide, or silicon nitride. As part of the semiconductor device fabrication process, these types of materials are normally deposited on the surface of a semiconductor device by typical methods such as electroplating or chemical vapor deposition and then removed and planarized using a CMP process. Prior art FIG. 2 is a perspective view of a CMP system used to perform a conventional CMP process with an exploded cross-sectional view 9 of a semiconductor device being planarized. In FIG. 2, the CMP system 5 includes a polishing pad 10, placed on a rotating table 12. The semiconductor wafer 14 containing the semiconductor device is held in a rotating carrier 16, and the front surface 17 of the semiconductor device on the wafer 14 is rubbed against the polishing pad 10 to planarize the semiconductor device.
During a conventional CMP process, a chemical liquid 18 is also required and is delivered to the CMP system 5 by a first delivery device 7. Although not shown, typically a fine particle abrasive such as alumina or silica, normally already mixed into the chemical liquid 18 and known conventionally as a slurry, is also required for the CMP process. The diameter of the abrasive particles typically ranges from ten nanometers to ten microns. The abrasive particles need not be already mixed in the chemical liquid 18, but rather may be embedded in the polishing pad 10. Alternatively, the abrasive particles may also be separately delivered to the CMP system 5 by a second delivery device (not shown) and mixed with the chemical liquid 18 on the polishing pad 10. In operation, the chemical liquid 18 and/or slurry is used to continuously wet the polishing pad 10 while the pad 10 is mechanically rubbed against the front surface 17 of the semiconductor device enabling removal and planarization of the deposited material on the wafer 14.
Recently, CMP and electroplating have received a tremendous and growing amount of investigation and engineering as enabling technologies for manufacturing high-speed semiconductor devices. This is because high-conductivity copper is now being used as the interconnect material (replacing aluminum) to connect multiple semiconductor devices on a semiconductor device. Electroplating has been used to deposit copper on semiconductor wafers. With the use of copper, more and more layers are formed on a single semiconductor device and in a more compact area. With the additional layers, the CMP and the electroplating processes are both used more frequently since each such layer requires metal deposition and planarization prior to adding subsequent layers. Thus, the electroplating and CMP processes are becoming increasingly more necessary as more layers are formed and increasingly more important to the overall semiconductor manufacturing process.
Two areas of concern in both the CMP and electroplating processes are the high cost of consumables used and the environmental impact of discarding used CMP and electroplating chemical liquids. In electroplating, the high cost of consumables generally stems from items that are xe2x80x9cconsumedxe2x80x9d during processing such as the electroplating chemical solution or the anode material that becomes dissolved during processing as described in FIG. 1. In CMP, the high cost of consumables generally stems from items such as the chemical liquid or slurry and polishing pads of FIG. 2, to name a few. For example, a copper CMP process may require about 600 cubic centimeters of chemical liquid for each semiconductor wafer processed. At this rate, a semiconductor manufacturing facility that produces 5,000 completed semiconductor wafers each week, and that requires six copper CMP processes for each completed semiconductor wafer, may require about one million liters of chemical liquid each year for the copper CMP process. At current slurry costs of about $10.00 per liter, this translates to a cost of over ten million dollars annually.
As mentioned above, disposal of the used CMP chemical liquids or the CMP effluent is another concern in CMP processing. Prior art FIG. 3 is a typical disposal system for CMP effluent in a semiconductor manufacturing facility. In Prior Art FIG. 3, a chemical liquid or slurry 20 contained in storage tank 25 is sent to the CMP system 30, such as the CMP system 5 of prior art FIG. 2. The xe2x80x9cusedxe2x80x9d slurry or chemical liquid from the CMP process flows through a drain 31 and is sent to a facility 35 for adherence to environmental regulations.
For a copper CMP process, the facility 35 might remove dissolved copper in order to meet Environmental Protection Agency (EPA) requirements for maximum permitted contamination or effluent levels. For example, these EPA requirements for maximum permitted effluent levels may be 0.6 parts per million. In a copper CMP process on semiconductor wafers of 200 millimeters in diameter, with a film of deposited copper that is one micrometer in thickness, the concentration of copper in the effluent produced during copper CMP processing would be about 500 parts per million. This effluent would likely require costly procedures to remove the copper contained in the effluent.
To relieve these concerns, several solutions have been suggested. For example, in U.S. Pat. Nos. 5,664,990 titled xe2x80x9cSlurry Recycling in CMP Apparatus,xe2x80x9d and 5,755,614 titled xe2x80x9cRinse Water Recycling in CMP Apparatus,xe2x80x9d a solution of capturing a used slurry (in one patent) and rinse water (in the other patent) after the CMP process to continuously blend the used slurry or rinse water with fresh slurry is disclosed. However, there is no disclosure in these patents for removing dissolved materials, such as dissolved copper, from the slurry or rinse water. Only a filtration system is disclosed that removes particles that have not been dissolved in the slurry or rinse water. Thus, the recycled slurry still contains much of the dissolved material that was removed from the semiconductor wafer during the CMP process, which, in turn, degrades the quality of the recycled slurry. Additionally, there is no mention in this patent of reclaiming a metal from the CMP effluent for use in an electroplating process.
U.S. Pat. No. 5,791,970 titled xe2x80x9cSlurry Recycling System for Chemical-Mechanical Polishing Apparatusxe2x80x9d also discloses a manner of recycling CMP slurry using an endpoint-monitoring system. The endpoint-monitoring system monitors the impact of the slurry on the removal rate of the CMP process and accordingly controls the rate of recycled slurry usage, thereby reducing any negative impact the recycled slurry may have on the CMP process. This solution, however, much like the prior patents discussed above, does not provide for removing the dissolved material found in the effluent that is removed from the surface of the semiconductor wafer. Again, the recycled slurry contains contaminated, dissolved materials that degrade the quality of the recycled slurry and affects the performance of the CMP process using that recycled slurry. Also, there is no mention in this patent of reclaiming a metal from the CMP effluent for use in an electroplating process.
A need therefore exists for a method in electroplating and in CMP that alleviates the high costs of consumables used and that reduces waste in such process. Any solution to this need must be capable of doing more than merely filtering particles in the slurry. The solution must be capable of removing dissolved materials from a used slurry or chemical liquid, and reusing the reclaimed chemical solution or reclaimed metal without having a detrimental impact on the performance of the CMP and/or electroplating processes.
The present invention provides for a method of reclaiming a metal from the effluent of a CMP process and using said reclaimed metal in an electroplating process. The invention also provides a method of rejuvenating a chemical solution used in a first CMP process for reuse in a second CMP process. This method is performed in three steps. A first step uses the chemical solution in a first CMP process to remove a metal material from a semiconductor device undergoing the first CMP process. This step produces an effluent that contains a dissolved first species removed from the semiconductor device during the first CMP process. The second step involves treating the effluent with a first electroplating process to remove the dissolved first species. This second step may produce a rejuvenated chemical solution that may then be used in a second CMP process. The second step causes the dissolved first species to be electroplated as a reclaimed metal. The third step uses the reclaimed metal in a second electroplating process.
The dissolved first species may include, for example, ions of copper, tungsten, aluminum, iron, nickel, titanium, tantalum, palladium, iridium, platinum, silver and the like.
In one embodiment of the present invention, as part of the treating step of the method of the present invention, the step of adding a second species, such as an oxidizer, to the rejuvenated chemical solution is included. This adding step, in this embodiment, may be performed before, after, or simultaneous to, the treating step of the method of the present invention.
In another embodiment of the treating step of the method of the present invention, ion exchanging is performed to remove the dissolved first species from the effluent.
In a further embodiment of the present invention, the treating step of the method of the present invention may be performed by precipitating the dissolved first species. In yet another embodiment, an additional filtering step is performed to remove particles from the effluent, which may also be removed using a centrifuging method.
The apparatus of the present invention includes, in one embodiment, a CMP means for removing material from a semiconductor device producing an effluent containing a dissolved first species, a first electroplating means for treating the effluent to remove the dissolved first species and produce a reclaimed metal, and a second electroplating means in which the reclaimed metal is used. The CMP means, in one embodiment, includes a polishing pad, a rotating table, a wafer containing a semiconductor device and a rotating carrier to hold the wafer. The CMP means further includes delivery devices to deliver a chemical solution to the wafer and a waste device to remove used chemical solutions from a CMP process. The first and second electroplating means, in one embodiment, each include an electroplating chemical solution, a chemical solution storage chamber, an electroplating chamber, an anode, a cathode, and a power source such as a battery or a potentiostat. In one embodiment, the cathode of the first electroplating means is used as the anode of the second electroplating means.
In another embodiment, the CMP means and the second electroplating means are separate chambers integrated together into a larger device.
It is noted that the CMP and electroplating means are not limited to the components described in this embodiment, but includes all well-known components used to CMP or electroplate materials. For example, instead of a rotating table and/or a rotating carrier, said CMP means may include any mechanism that can cause the relative motion of the wafer against the polishing pad. As another example, the CMP and/or electroplating means may include components for cleaning and/or drying the surfaces of the materials either during or after processing. Such components may include, brush scrubbers, megasonic devices, and/or spin-rinse dryers.
In several embodiments an ion exchange device, a filtering device, and/or a centrifuging device are used to treat the effluent from the CMP process. The ion exchange device performs the well-known procedure where a material (e.g. resin) in a system removes a first ion while a second ion is introduced to the system to thereby xe2x80x9cexchangexe2x80x9d the ions. The filtering device and the centrifuging device each perform the well-known procedure of removing a solid particle from the CMP effluent. In one embodiment, the ion exchange device and the filtering device are used in addition to the electroplating device to produce a rejuvenated chemical solution and a reclaimed metal.